As is known, a helicopter substantially comprises a fuselage defining a cockpit at the front and housing the equipment of the helicopter; a main rotor fitted to the top of a central portion of the fuselage, and which generates a force to sustain and control the direction of the helicopter; and a tail rotor cooperating with the main rotor to manoeuvre the helicopter.
The fuselage is connected to the main rotor, which sustains the entire helicopter, by means of a number of connecting rods, i.e. is “suspended” by the rods from the outer casing of the main rotor pylon.
In the following description, only the main rotor of the helicopter is referred to, and, for the sake of simplicity, is therefore referred to simply as “rotor” as opposed to “main rotor”.
As is known, operation of the rotor induces vibration in the fuselage via the connecting rods, thus resulting in discomfort to the crew and dynamic stress of the fuselage itself.
To reduce such vibration, helicopters may be equipped with a control device for determining quantities associated with vibration of the fuselage, and generating a force field on the fuselage to counteract vibration.
More specifically, known control devices comprise a number of accelerometers for generating respective signals associated with acceleration of predetermined points of the fuselage; one or more actuators which act on the fuselage to generate said force field; and an electronic unit which receives the signals generated by the accelerometers, and generates a control signal for controlling the actuators.
Though efficient, control devices of the type described leave room for further improvement, particularly as regards the need felt in the industry to reduce the energy consumption, size and weight of the equipment of the helicopter, without imposing excessive design restrictions.
In particular, known actuators are unsatisfactory in reducing vibration of the fuselage areas further away from the areas in which the force field is applied, thus resulting in non-homogeneous vibration of different areas of the fuselage.
As a result, crew location is dependent on the areas in which the force field is applied by the actuators.
Moreover, vibration of the fuselage is greater in the areas further away from the point at which the fuselage is connected to the connecting rods. And reducing vibration in these areas requires that a particularly strong force field be generated by the actuators, and therefore actuators of greater weight, size, and energy consumption.
Since the force field generated by the actuators on the fuselage has an alternating pattern, the fuselage areas on which the force field is exerted are subjected to fatigue stress and must therefore be greater in size and weight.